With the master molecule of heredity, deoxyribonucleic acid (or DNA), so frequently mentioned in the media — in connections ranging from polymerase chain reaction (PCR) applications (e.g., criminology, medical diagnoses) to cloning and art  — it is difficult to imagine today that it was only a few decades ago when Watson and Crick reported their description of the DNAdouble helix [1354–1356]! Based on analysis of DNA fiber diffraction patterns and Chargaff’s rules, they described a spiral image of an orderly helix — two intertwined polynucleotide chains, with a sugar/phosphate backbone on the exterior and pairs of hydrogen-bondednitrogenous bases in the center. See  for a historical perspective of this discovery, including the contribution of all key players (a capsule of which is given in Chapter 1), and anniversary issues of DNA, for example issued in 2003 in many journals (e.g., Nature Vol. 421 and Science Vol. 300) at the occasion of DNA’s golden anniversary.